vold: use system-clang-format

vold: use system-clang-format

Link .clang-format to the standard .clang-format file (4-space-indent
version) from build/soong, rather than use a custom file.

Among other changes, the standard file has the "IncludeBlocks: Preserve"
setting, so include blocks stay in order.

Don't actually reformat all the code yet.

Test: Tried 'clang-format -i $(find . -name \*.cpp -o -name \*.h)'
      and checked that the changes look sane.
Change-Id: I11ecbd03b31e44ba7b3e01175a6fc317f8173ab0